There is no such exception. Banks are free to do business with whomever they wish. Direktbanken are usually probably the hardest to open an account with if you are a resident abroad.
Deutsche Bank is well known for offering accounts to non-residents. Pretty much any Sparkasse will open an account for you if you walk in even without a German address.
The list of banks that don't offer accounts to non-residents is probably shorter than the other. Granted, these are mostly the ones with the best offers.